Error Found : System.InvalidOperationException: Operations that change non-concurrent collections must have exclusive access. A concurrent update was performed on this collection and corrupted its state. The collection's state is no longer correct. at System.Collections.Generic.Dictionary`2.FindValue(TKey key) at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value) at System.Net.Http.Headers.HttpHeaders.TryGetAndParseHeaderInfo(HeaderDescriptor key, HeaderStoreItemInfo& info) at System.Net.Http.Headers.HttpHeaders.PrepareHeaderInfoForAdd(HeaderDescriptor descriptor, HeaderStoreItemInfo& info, Boolean& addToStore) at AdsPortalClientApi.ApiClient.addHeaders(Boolean bAddHeader) in F:\Development\AdsPortal\AdsPortalClientApi\ApiClient.cs:line 90 at AdsPortalClientApi.ApiClient.GetAsync[T](Uri requestUrl) in F:\Development\AdsPortal\AdsPortalClientApi\ApiClient.cs:line 34 at AdsPortalClientApi.ApiClient.GetProduct(Int32 iProductId) in F:\Development\AdsPortal\AdsPortalClientApi\ProductClient.cs:line 79 at AdsPortals.ProductController.DetailProduct(Int32 id) in F:\Development\AdsPortal\AdsPortal\Controllers\ProductController.cs:line 57